diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index e82d49dfa8109c51c2c60943a38c9f66b5b385e0..4e4d89a00e8432cdcaeae6960dceefa6e62ce589 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -28,10 +28,10 @@ variables:
 
 ## Build jobs
 
-build-coq.8.17.0:
+build-coq.8.18.0:
   <<: *template
   variables:
-    OPAM_PINS: "coq version 8.17.0"
+    OPAM_PINS: "coq version 8.18.0"
     DENY_WARNINGS: "1"
     MANGLE_NAMES: "1"
   tags:
@@ -40,7 +40,7 @@ build-coq.8.17.0:
 trigger-iris.timing:
   <<: *template
   variables:
-    OPAM_PINS: "coq version 8.17.0   git+https://gitlab.mpi-sws.org/$IRIS_REPO#$IRIS_REV"
+    OPAM_PINS: "coq version 8.18.0   git+https://gitlab.mpi-sws.org/$IRIS_REPO#$IRIS_REV"
   tags:
   - fp-timing
   only:
diff --git a/README.md b/README.md
index d7439865d5014e430cd9ea85fa38a7128ad4e35d..89744a06f5b5a72c172d4efb6e2e62a5f41a54ff 100644
--- a/README.md
+++ b/README.md
@@ -6,7 +6,7 @@ This is the Coq development accompanying lambda-Rust.
 
 This version is known to compile with:
 
- - Coq 8.17.0
+ - Coq 8.18.0
  - A development version of [Iris](https://gitlab.mpi-sws.org/iris/iris)
 
 ## Building from source
diff --git a/theories/lang/heap.v b/theories/lang/heap.v
index ba10b34fc37f188c343c636203533bf51e22485f..784b32e675d50de99b0a7d43e9b09b93f77a3e83 100644
--- a/theories/lang/heap.v
+++ b/theories/lang/heap.v
@@ -91,7 +91,7 @@ Section to_heap.
   Implicit Types σ : state.
 
   Lemma to_heap_valid σ : ✓ to_heap σ.
-  Proof. intros l. rewrite lookup_fmap. case (σ !! l)=> [[[|n] v]|] //=. Qed.
+  Proof. intros l. rewrite lookup_fmap. destruct (σ !! l) as [[[|n] v]|] eqn:EQ; rewrite EQ //. Qed.
 
   Lemma lookup_to_heap_None σ l : σ !! l = None → to_heap σ !! l = None.
   Proof. by rewrite /to_heap lookup_fmap=> ->. Qed.